Here is my beautiful HK416A5 (€700) with a maximum of about 1000 bb's through it, it shoots like a gem. I had this replica because I thought I might try airsoft, and upgraded it over time.
With a nice EOTech Holo and G33 Magnifier REPLICA (€170), and a nice m4 mag with matching cover (€90) for more style AND more grip. An Angled Grip OR for the enthusiast a Vertical Grip (€20). To top it off, of course, a nice silencer. (€80)
Since the original mag has a gas leak (easy to fix for experienced people, I was told before) and the new mag is missing a piece after a fall that indicates when it is empty, I understand that the value of both mags goes down.
But for such a gem that has never been outside (except my backyard), I expect normal prices. Of course, after a little chat, you can come and shoot in my backyard and see what you think.